System and method for controlling valve timing of continuous variable valve duration engine

ABSTRACT

A method for controlling intake and exhaust valves of an engine includes: controlling, by an intake continuous variable valve timing (CVVT) device, opening and closing timings of the intake valve; controlling, by an exhaust CVVT device, opening and closing timing of the exhaust valve; determining, by a controller, first to fifth control regions based on engine load and speeds, and a target opening duration of the intake valve and target opening or target closing timings of the intake valve; modifying, by an intake continuous variable valve duration (CVVD) device, current opening and closing timings of the intake valve based on the target opening duration; and advancing or retarding, by the intake CVVD device, the current opening timing of the intake valve while simultaneously retarding or advancing the current closing timing of the intake valve by a predetermined value based on the target opening duration of the intake valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 15/340,778, filed on Nov. 1, 2016, and claims priority to and the benefit of Korean Patent Application Nos. 10-2015-0175141, filed on Dec. 9, 2015, and 10-2017-0154705, filed on Nov. 20, 2017, the entirety of each of which are incorporated herein by reference.

FIELD

The present disclosure relates to a system and a method for controlling valve timing of a continuous variable valve duration engine.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

An internal combustion engine combusts mixed gas in which fuel and air are mixed at a predetermined ratio through a set ignition mode to generate power by using explosion pressure.

Generally, a camshaft is driven by a timing belt connected with a crankshaft that converts linear motion of a piston by the explosion pressure into rotating motion to actuate an intake valve and an exhaust valve, and while the intake valve is opened, air is suctioned into a combustion chamber, and while an exhaust valve is opened, gas which is combusted in the combustion chamber is exhausted.

To improve the operations of the intake valve and the exhaust valve and thereby improve engine performance, a valve lift and a valve opening/closing time (timing) are controlled according to a rotational speed or load of an engine. Therefore, a continuous variable valve duration (CVVD) device controlling opening duration of an intake valve and an exhaust valve of the engine and a continuous variable valve timing (CVVT) device controlling opening timing and closing timing of the intake valve and the exhaust valve of the engine have been developed.

The CVVD device adjusts opening duration of the valve. In addition, the CVVT device advances or retards the opening and closing timing of the valve in a state in which the duration of the valve is fixed. In other words, when the opening timing of the valve is determined, the closing timing is automatically determined according to the duration of the valve.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure provides a system and a method for controlling valve timing of a continuous variable valve duration engine having advantages of simultaneously controlling duration and timing of the continuous variable valve by mounting a continuous variable valve duration device and a continuous variable valve timing device on an intake and mounting a continuous variable valve timing device on an exhaust.

In one form of the present disclosure, a method for controlling intake and exhaust valves of an engine includes: controlling, by an intake continuous variable valve timing (CVVT) device, opening and closing timings of the intake valve; controlling, by an exhaust CVVT device, opening and closing timing of the exhaust valve; determining, by a controller, a target opening duration of the intake valve and at least one of a target opening timing or a target closing timing of the intake valve and the exhaust valve, based on an engine load and an engine speed; modifying, by an intake continuous variable valve duration (CVVD) device, current opening and closing timings of the intake valve based on the target opening duration of the intake valve; and advancing, by the intake CVVD device, the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake valve by a predetermined value, or retarding the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve by a predetermined value, based on the target opening duration of the intake valve.

In particular, the intake CVVD device advances the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake valve when the target opening duration of the intake valve is longer than a duration between the current opening timing and current closing timing of the intake valve.

The intake CVVD device retards the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve when the target opening duration of the intake valve is shorter than a duration between the current opening timing and current closing timing of the intake valve.

The method further includes the step of adjusting, by the intake CVVT device, the current opening and closing timings of the intake valve to the target opening and closing timings of the intake valve, respectively.

During the step of determining the target opening duration of the intake valve, the controller sets the target opening duration of the intake valve to a first intake opening duration in a first control region where the engine load is between first and second predetermined loads, and the controller controls the intake CVVD device to adjust a current opening duration to the first intake opening duration and controls a valve overlap between the intake valve and the exhaust valve in the first control region.

The current opening and closing timings of the intake valve are fixed and the closing timing of the exhaust valve is set as a maximum value capable of maintaining combustion stability in the first control region.

During the step of determining the target opening duration of the intake valve, the controller sets the target opening duration of the intake valve to a second intake opening duration in a second control region where the engine load is greater than the second predetermined load and equal to or less than a third predetermined load, and the controller reduces a valve overlap by advancing the current closing timing of the exhaust valve via the exhaust CVVT device in the second control region.

In one form, a retardation amount of the current closing timing of the exhaust valve is reduced based on an increase of the engine load in the second control region.

The method further includes the step of advancing the current closing timing of the intake valve via the intake CVVT device according to an increase of the engine load in a third control region where the engine load is greater than a third predetermined load and equal to or less than a fourth predetermined load.

The method further includes the step of controlling, by the controller, a throttle valve to be fully opened; and controlling the current closing timing of the exhaust valve to be an angle after a top dead center (TDC) in a fourth control region where the engine load is greater than a fourth predetermined load and equal to or less than a fifth predetermined load and the engine speed is between first and second predetermined speeds.

In another form, the method may include: the step of determining a fifth control region when the engine load is greater than a fourth predetermined load and equal to or less than a fifth predetermined load and the engine speed is greater than a second predetermined speed and equal to or less than a third predetermined speed; and the step of controlling, by the controller, a throttle valve to be fully opened and the current closing timing of the intake valve according to the engine speed in the fifth control region.

The target opening duration of the intake valve is increased according to an increase of the engine speed by retarding the current opening and closing timings of the intake valve in the fifth control region.

The exhaust CVVT device controls the current closing timing of the exhaust valve to be approximately at a top dead center so as to inhibit a valve overlap in the fifth control region.

According to one form of the present disclosure, duration and timing of the continuous variable valve are simultaneously controlled, so the engine may be controlled under desirable conditions.

That is, since opening timing and closing timing of the intake valve and the exhaust valve are appropriately controlled, the fuel efficiency under a partial load condition and power performance under a high load condition are improved. In addition, a fuel amount for starting may be reduced by increasing a valid compression ratio, and exhaust gas may be reduced by shortening time for heating a catalyst.

Further, a fixed cam may be used instead of a continuous variable valve duration device in the exhaust, thereby reducing the additional cost.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a schematic block diagram showing a system for controlling valve timing of a continuous variable valve duration engine according to one form of the present disclosure;

FIG. 2 is a perspective view showing an intake provided with a continuous variable valve duration device and a continuous variable valve timing device and an exhaust provided with a continuous variable valve timing device according to one form of the present disclosure;

FIG. 3 is a side view of a continuous variable valve duration device assembled with a continuous variable valve timing device in another form;

FIG. 4 is a partial view of an inner wheel and a cam unit of a continuous variable valve duration device in one form;

FIGS. 5A-5C are views illustrating the operation of an intake continuous variable valve duration device in FIG. 4;

FIGS. 6A and 6B are views illustrating a cam slot of an intake continuous variable valve duration device in exemplary forms;

FIGS. 7A-7C are valve profiles of an intake continuous variable valve duration device in one form;

FIGS. 8A-8D illustrate a change of an opening duration and opening and closing timings of a valve;

FIGS. 9A and 9B are flowcharts showing a method for controlling valve timing of a continuous variable valve duration engine according to one form of the present disclosure;

FIG. 10 is a schematic diagram illustrating control regions in one form;

FIGS. 11A-11C are graphs showing duration, opening timing, and closing timing of an intake valve depending on an engine load and an engine speed in one form of the present disclosure; and

FIGS. 12A-12C are graphs showing duration, opening timing, and closing timing of an exhaust valve depending on an engine load and an engine speed in one form of the present disclosure.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

As those skilled in the art would realize, the described forms may be modified in various different ways, all without departing from the spirit or scope of the present disclosure.

Throughout this specification and the claims which follow, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

It is understood that the term “vehicle” or “vehicular” or other similar terms as used herein is inclusive of motor vehicles in general including hybrid vehicles, plug-in hybrid electric vehicles, and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid electric vehicle is a vehicle that has two or more sources of power, for example a gasoline-powered and electric-powered vehicle.

Additionally, it is understood that some of the methods may be executed by at least one controller. The term controller refers to a hardware device that includes a memory and a processor configured to execute one or more steps that should be interpreted as its algorithmic structure. The memory is configured to store algorithmic steps, and the processor is specifically configured to execute said algorithmic steps to perform one or more processes which are described further below.

Furthermore, the control logic of the present disclosure may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, a controller, or the like. Examples of computer readable media include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards, and optical data storage devices. The computer readable recording medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a controller area network (CAN).

FIG. 1 is a schematic block diagram showing a system for controlling valve timing of a continuous variable valve duration engine according to an exemplary form of the present disclosure.

As shown in FIG. 1, a system for controlling valve timing of a continuous variable valve duration engine according to an exemplary form of the present disclosure includes a data detector 100, a camshaft position sensor 120, a controller 300, an intake continuous variable valve duration device 400, an intake continuous variable valve timing device 450, an exhaust continuous variable valve timing device 550, and a throttle valve 600, although other sensors or systems may be employed to detect or determine the desired data.

The data detector 100 detects data related to a running state of the vehicle for controlling the CVVD device and the CWT devices, and includes a vehicle speed sensor 111, an engine speed sensor 112, an oil temperature sensor 113, an air flow sensor 114, and an accelerator pedal position sensor (APS) 115.

The vehicle speed sensor 111 detects a vehicle speed, and transmits a signal corresponding thereto to the controller 300. The vehicle speed sensor 111 may be mounted at a wheel of the vehicle.

The engine speed sensor 112 detects an engine speed from a change in phase of a crankshaft or camshaft, and transmits a signal corresponding thereto to the controller 300.

The oil temperature sensor (OTS) 113 detects temperature of oil flowing through an oil control valve (OCV), and transmits a signal corresponding thereto to the controller 300.

The oil temperature detected by the oil temperature sensor 113 may be determined by determining a coolant temperature using a coolant temperature sensor mounted at a coolant passage of an intake manifold. Therefore, in one form, the oil temperature sensor 113 may include the coolant temperature sensor, and the oil temperature should be understood to be the coolant temperature.

The air flow sensor 114 detects an air amount flowing into the intake manifold, and transmits a signal corresponding thereto to the controller 300.

The accelerator pedal position sensor 115 detects a degree at which a driver pushes an accelerator pedal, and transmits a signal corresponding thereto to the controller 300. A position value of the accelerator pedal is 100% when the accelerator pedal is pressed fully, and the position value of the accelerator pedal is 0% when the accelerator pedal is not pressed at all.

A throttle valve position sensor that is mounted on an intake passage may be used instead of the accelerator pedal position sensor 115. Therefore, in one form, the accelerator pedal position sensor 115 may include the throttle valve position sensor, and the position value of the accelerator pedal should be understood to be an opening value of the throttle value.

The camshaft position sensor 120 detects a position of a camshaft angle, and transmits a signal corresponding thereto to the controller 300.

FIG. 2 is a perspective view showing an intake provided with a continuous variable valve duration device and a continuous variable valve timing device and an exhaust provided with a continuous variable valve timing device according to one form of the present disclosure.

As shown in FIG. 2, the continuous variable valve duration device and the continuous variable valve timing device are mounted on the intake, and the continuous variable valve timing device is mounted on the exhaust through a fixed cam. Therefore, exhaust valve duration (EVD) is fixed. If the EVD becomes long, fuel efficiency and high speed performance of the vehicle may be improved, but low speed performance may be deteriorated. Thus, the EVD may be fixed at an angle of approximately 220 to 240 degrees.

The intake continuous variable valve duration (CVVD) device 400 controls opening duration of an intake valve of the engine according to a signal from the controller 300.

FIG. 3 is a side view of the intake CVVD device in another form as assembled with the intake CVVT for intake valves 200 operating with cylinders 201, 202, 203, 204. In one form, two cams 71 and 72 may be formed on first and second cam portions 70 a and 70 b, and a cam cap engaging portion 76 may be formed between the cams 71 and 72 and supported by a cam cap 40. The valve 200 is opened and closed by being in contact with the cams 71 and 72.

As illustrated in FIG. 3, the intake CVVD device includes: a cam unit 70 in which a cam 71 is formed and into which a cam shaft 30 is inserted; an inner wheel 80 to transfer the rotation of the cam shaft 30 to the cam unit 70 (See, in FIG. 4); a wheel housing 90 in which the inner wheel 80 rotates and movable in a direction perpendicular to the camshaft 30; a guide shaft 132 having a guide thread and provided in a direction perpendicular to the camshaft 30, the guide shaft mounted by a guide bracket 134; a worm wheel 50 having an inner thread engaged with the guide thread and disposed inside the wheel housing 90; and a control shaft 102 formed with a control worm 104 meshing with the worm wheel 50. The control worm 104 is engaged with an outer thread formed on the outer side of the worm wheel 50. The intake CVVD device further includes a sliding shaft 135 fixed to the guide bracket 134 and guiding the movement of the wheel housing 90.

FIG. 4 is a partial view of the inner wheel 80 and the cam unit 70 of the intake CVVD device of the FIG. 3. Referring to FIG. 4, First and second sliding holes 86 and 88 are formed in the inner wheel 80, and a cam slot 74 is formed in the cam unit 70.

The intake CVVD device further includes: a roller wheel 60 inserted into the first sliding hole 86 allowing the roller wheel 60 to rotate; and a roller cam 82 inserted into the cam slot 74 and the second sliding hole 88. The roller cam 82 may slide in the cam slot 74 and rotate in the second sliding hole 88.

The roller cam 82 includes: a roller cam body 82 a slidably inserted into the cam slot 74 and a roller cam head 82 b rotatably inserted into the second sliding hole 88.

The roller wheel 60 includes: a wheel body 62 slidably inserted into the camshaft 30 and a wheel head 64 rotatably inserted into the first sliding hole 86. A cam shaft hole 34 is formed in the camshaft 30 and a wheel body 62 of the roller wheel 60 is movably inserted into the camshaft hole 34.

FIGS. 5A-5C illustrate the operation of the intake CVVD device. FIG. 5A illustrates a neutral state in which the rotational center of the camshaft 30 and the cam unit 70 coincide with each other. In this case, the cams 71 and 72 rotate at the same speed as the camshaft 30. When the controller 300 applies a control signal based on engine load and/or engine speed, a control motor 106 rotates the control shaft 102. Then, the control worm 104 rotates the worm wheel 50 which in turn rotates and moves along the guide thread formed on the guide shaft 132.

As a result, the worm wheel 50 causes a change to a position of the wheel housing 90 relative to the cam shaft 30. As illustrated in FIGS. 5B and 5C, when the position of the wheel housing 90 moves in one direction with respect to the center of rotation of the camshaft 30, the rotational speed of the cams 71, 72 with respect to the camshaft 30 are changed in accordance with their phases. FIG. 7A and FIG. 8B are drawings showing a valve profile illustrating valve opening duration change by the operation of the intake CVVD device. The solid line represents a general valve profile (e.g., a current opening duration), and the dotted line shows the valve profile as a short opening duration (e.g., a target opening duration in FIG. 8B) is applied. FIG. 8A illustrates a changed valve profile when the long opening duration is applied by the CVVD device. The controller 300 determines a target opening duration based on an engine load and an engine speed and controls the intake CVVD device to modify current opening and closing timings of the intake valve based on the target opening duration.

More specifically, as illustrated in FIG. 8B, the intake CVVD device may retard the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve to shorten the opening duration according to a predetermined value provided by the controller 300. When the controller applies a longer opening duration (i.e., a target opening duration) than the current opening duration, as illustrated in FIG. 8A, the CVVD device may advance the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake vale so that the modified opening duration becomes longer than the current opening duration. FIGS. 8C and 8D illustrate the relationship between the operation of the CVVD device and the CVVT device. As discussed above, the CVVD device may change the opening duration of a valve (e.g., intake or exhaust valve) whereas the CVVT device may shift a valve profile according to a target opening and/or a target closing timings without change to the period of the valve opening duration. It should be noted that the changing opening duration by the CVVD device may occur after changing valve opening and/or closing timings of intake or exhaust valves by the CVVT device. In another form, the operation of the CVVT device to change the opening and closing timings may occur after the operation of the CVVD device. In still another form, the operation of the CVVD and CVVT devices may perform simultaneously to change the opening duration and the timing of opening and closing of intake or exhaust valves.

FIGS. 6A and 6B illustrate a view of the cam slot 74 a, 74 b of the intake CVVD device, and FIGS. 7A-7C illustrate valve profiles of the CVVD device in exemplary forms of the present disclosure.

Referring to FIGS. 6A-6B, the cam slot 74 a may be formed in an advanced position relative to the cam 71, 72, or in another form the cam slot 74 b may be formed in a retarded position relative to the cam 71, 72. In another form, the cam slot 74 a, 74 b may be formed to have the same phase as the lobe of the cam 71, 72. These variations are enable to realize various valve profiles. Based on the position of the cam slot 74 a, 74 b, and a contact position between the cam and the intake valve, the opening and closing timings of the intake valve may vary. FIG. 7B shows that the intake CVVD device may advance (for a short opening duration) or retard the current closing timing (for a long opening duration) of the intake valve by a predetermined value based on the target opening duration of the intake valve while maintaining the current opening timing of the intake valve. In another form, as illustrated in FIG. 7C, the intake CVVD device may advance (for a long opening duration) or retard (for a short opening duration) the current opening timing of the intake valve by a predetermined value based on the target opening duration of the intake valve while maintaining the current closing timing of the intake valve.

The intake continuous variable valve timing (CVVT) device 450 controls the opening timing and closing timing of the intake valve of the engine according to a signal from the controller 300, and the exhaust continuous variable valve timing (CVVT) device 550 controls the opening timing and closing timing of an exhaust valve of the engine according to a signal from the controller 300.

The throttle valve 600 adjusts the amount of air flowing into the intake manifold.

The controller 300 classifies a plurality of control regions depending on an engine speed and an engine load based on signals of the data detector 100 and the camshaft position sensor 120, and controls operations of the intake CVVD device 400, the intake CVVT device 450, the exhaust CVVT device 550, and the throttle valve 600. Herein, the plurality of control regions may be classified into five regions.

The controller 300 applies a maximum duration (i.e., a target opening duration) to the intake valve and controls valve overlap between the exhaust valve and the intake valve in a first control region, applies the maximum duration to the intake valve and controls the valve overlap to be reduced by using exhaust valve closing (EVC) timing in a second control region, advances intake valve closing (IVC) timing according to an increase of the engine load in a third control region, controls the throttle valve to be fully opened and controls the EVC timing to an angle after top dead center (TDC) in a fourth control region, and controls the throttle valve to be fully opened and controls the IVC timing according to the engine speed in a fifth control region.

For these purposes, the controller 300 may be implemented with at least one processor executed by a predetermined program, and the predetermined program may programmed in order to perform each step of a method for controlling valve timing of a continuous variable valve duration engine.

Various forms described herein may be implemented within a recording medium that may be read by a computer or a similar device by using software, hardware, or a combination thereof.

For example, the hardware of the forms described herein may be implemented by using at least one of application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and electrical units designed to perform any other functions.

The software such as procedures and functions of the forms described in the present disclosure may be implemented by separate software modules. Each of the software modules may perform one or more functions and operations described in the present disclosure. A software code may be implemented by a software application written in an appropriate program language.

Hereinafter, a method for controlling valve timing of a continuous variable valve duration engine according to one form of the present disclosure will be described in detail with reference to FIG. 9A to FIG. 12C.

FIGS. 9A and 9B are flowcharts showing a method for controlling valve timing of a continuous variable valve duration engine. FIG. 10 is a schematic block diagram of showing control regions based on engine load (e.g., engine torque) and engine speed. In addition, FIGS. 11A-11C are graphs showing duration, opening timing, and closing timing of an intake valve depending on an engine load and an engine speed, and FIGS. 12A-12C are graphs showing duration, opening timing, and closing timing of an exhaust valve depending on an engine load and an engine speed.

As shown in FIGS. 9A and 9B, a method for controlling valve timing of a continuous variable valve duration engine begins with classifying a plurality of control regions depending on an engine load and an engine speed at step S100. The control region may be divided into five control regions (e.g., first, second, third, fourth, and fifth control regions). The first to fifth control regions are indicated in FIG. 10, and FIG. 11A to FIG. 12C in more detail. FIG. 10 schematically describes the control regions based on the engine load (e.g., engine torque) and engine speed (e.g., revolutions per minutes “rpm”). However, the control regions may vary based on engine type or engine size. Mixed control may be performed at the boundary of each region to minimize the control impact of the engine. Accordingly, the range of each region shown in the present application is exemplary, and the classification of each region may be varied.

The controller 300 may determine a control region as the first control region (namely, {circle around (1)} an idling region and low-load condition) when the engine load is between a first predetermined load (e.g., a minimum engine torque) and a second predetermined load, a second control region (namely, {circle around (2)} an mid-load condition) when the engine load is greater than the second predetermined load and equal to or less than a third predetermined load, and a third control region (namely, {circle around (3)} a high-load condition) where the engine load is greater than the third predetermined load and less than a fourth predetermined load.

In addition, the controller 300 may determine a control region as the fourth control region (namely, {circle around (4)} a low-speed wide open throttle “WOT” condition) when the engine load is greater than the fourth predetermined load (i.e., a maximum torque at the idle rpm) and equal to or less than the fifth predetermined load (i.e., a maximum torque) and the engine speed is between a first predetermined speed (i.e., the idle rpm) and a second predetermined speed, and determine the fifth control region (namely, {circle around (5)} a mid-high speed WOT condition) when the engine load is greater than the fourth predetermined load and equal to or less than the fifth predetermined load and the engine speed is greater than the second predetermined speed and equal to or less than a third predetermined speed (i.e., an engine maximum rpm).

Referring to FIG. 10, the first predetermined load (e.g., a minimum engine torque) is measured when a input from the APS is zero “0,” and the second to fifth predetermined loads, and the second and third predetermined engine speeds may be calculated by the following equations:

Second predetermined load=min_L+((⅖)×(max_L@idle_rpm-min_L);

Third predetermined load=min_L+(⅘)×(max_L@idle_rpm−min_L);

Fourth predetermine load=max_L@idle_rpm;

Fifth predetermined load=max_L;

Second predetermined engine speed=min_S+( 3/10)×(max_S−min_S); and

Third predetermined engine speed=max_S,

where, min_L is the minimum engine torque; max_L@idle_rpm is a maximum engine torque at a minimum engine rpm (i.e., Idle rpm); max_L is a maximum engine torque; min_S is a minimum engine rpm (e.g., Idle rpm); and max_S is a maximum engine rpm.

Meanwhile, as shown in FIG. 11A to FIG. 12C, a crank angle is indicated in intake valve duration (IVD) map and an exhaust valve duration (EVD) map. For example, regarding the IVD map, a curved line indicated by ‘200’ in the fifth control region means that the crank angel is approximately 200 degrees, and a curved line indicated by ‘220’ means that the crank angle is approximately 220 degrees. Although not illustrated in FIG. 11A-11C, a curved line having a crank angle between approximately 200 and 220 degrees may exist between the curved lines.

In addition, a number designated in an intake valve opening (IVO) timing map represents before top dead center (TDC), a number designated an intake valve closing (IVC) timing map represents after bottom dead center (BDC), a number designated in an exhaust valve opening (EVO) timing map represents before BDC, and a number designated in an exhaust valve closing (EVC) timing map represents after TDC.

Regions and curved lines shown in FIG. 11A to FIG. 12C are just examples for describing one form of the present disclosure, and the present disclosure is not limited thereto.

When the control regions are classified depending on the engine load and the engine speed at step S100, the controller 300 determines whether a current engine state belongs to the first control region at step S110.

When the engine load is between a first predetermined load (i.e., minimum load, or idle load) and the second predetermined load at step S110, the controller 300 determines that the current engine state belongs to the first control region. In this case, the controller 300 applies the maximum duration or a first intake opening duration to the intake valve and controls the valve overlap between the exhaust valve and the intake valve at step S120. The valve overlap represents a state in which the intake valve is opened and the exhaust valve is not yet closed.

In other words, when the engine is operated at a low load condition, the controller 300 may fix the IVO timing and the IVC timing to apply the maximum duration to the intake valve. In other words, the controller 300 controls the intake CVVD device to adjust a current opening duration to the first intake opening duration by advancing the IVO timing and retarding the IVC timing. As shown in FIGS. 11B and 11C, the IVO timing may be fixed at an angle of approximately 0 to 10 degrees before TDC, and the IVC timing may be fixed at an angle of approximately 100 to 110 degrees after BDC.

In addition, the controller 300 may set the EVC timing as a maximum value capable of maintaining combustion stability by moving the EVC timing in an after TDC direction. As the valve overlap is increased, fuel efficiency may be improved, but combustion stability may be deteriorated. Accordingly, properly setting of the valve overlap is desired. By setting the EVC timing as the maximum value capable of maintaining combustion stability, a valve overlap may be realized, and thus fuel efficiency may be improved.

When the current engine state does not belong to the first control region at step S110, the controller 300 determines whether the current engine state belongs to the second control region at step S130. However, each of the control regions may be determined immediately by the controller 300 based on the engine load and/or engine speed.

When the engine load is greater than the second predetermined load and equal to or less than the third predetermined load at step S130, the controller 300 determines that the current engine state belongs to the second control region. In this case, the controller 300 applies the maximum duration to the intake valve and controls the valve overlap to be reduced by using the EVC timing at step S140.

When the EVC timing is retarded in the after TDC direction, as the valve overlap is increased, intake pumping may be decreased, however, since the exhaust valve duration (EVD) is fixed, exhaust pumping may be increased as the EVO timing approaches BDC. In addition, the exhaust pumping may be increased as the engine load is increased in the second control region. Accordingly, the controller 300 may reduce the valve overlap by reducing retardation amount of the EVC timing according to an increase of the engine load.

In addition, the controller 300 may apply the maximum duration to the intake valve to prevent or inhibit knocking according to the increase of the engine load, and maintain a late intake valve close (LIVC) position at the angle of approximately 100 to 110 degrees after BDC.

When the current engine state does not belong to the second control region at step S130, the controller 300 determines whether the current engine state belongs to the third control region at step S150.

When the engine load is greater than a third predetermined load and equal to or less than a fourth predetermined load (i.e., a maximum torque at engine idle rpm), the controller 300 determines that the current engine state belongs to the third control region. In this case, the controller 300 advances the IVC timing according to the increase of the engine load at step S160.

In this case, the controller 300 may fix the exhaust CVVT device at a locking position by fixing the EVC timing.

When the current engine state does not belong to the third control region at step S150, the controller 300 determines whether the current engine state belongs to the fourth control region at step S170. In another form, the controller 300 may determine the condition for the fourth control region without performing the step of determining the first, second and third control regions.

The controller 300 determines that the current engine state belongs to the fourth control region when the engine load is greater than the fourth predetermined load and equal to or less than a fifth predetermined load (i.e., engine maximum torque) and the engine speed is between a first predetermined speed (i.e., idle rpm) and a second predetermined speed. In this case, the controller 300 controls the throttle valve to be fully opened and controls the EVC timing to an angle after TDC at step S180.

Since the engine speed is less than the predetermined speed (e.g., approximately 1500 rpm) in the fourth control region, the EVO timing should be close to BDC so as to reduce exhaust interference. Since the EVD is fixed in one form of the present disclosure, the controller 300 may control the EVC timing to an angle after TDC.

When the current engine state does not belong to the fourth control region at step S170, the controller 300 determines whether the current engine state belongs to the fifth control region at step S190.

When the engine load is greater than the fourth predetermined load and equal to or less than the fifth predetermined load and the engine speed is greater than the second predetermined speed and equal to or less than a third predetermined speed (i.e., a maximum rpm) at step S190, the controller 300 determines that the current engine state belongs to the fifth control region. In this case, the controller 300 controls the throttle valve to be fully opened and controls the IVC timing according to the engine speed at step S200.

The controller 300 may increase the IVD according to the increase of the engine speed by retarding the IVO timing and the IVC timing. Since the IVC timing may be a significant factor in the fifth control region where the engine speed is equal to or greater than the predetermined speed (e.g., approximately 1500 rpm), the IVC timing is firstly controlled to a desired value according to the engine speed. The IVC timing may be gradually retarded from an angle of approximately 20 degrees to an angle of approximately 60 degrees after BDC according to the increase of the engine speed.

In this case, the controller 300 may generate a valve underlap by retarding the IVO timing in a medium speed (e.g., approximately 1500-3000 rpm). Accordingly, the IVD may be decreased and then increased when the engine speed increases.

In addition, the controller 300 may control the EVC timing to be close to the TDC to prevent from generating the valve overlap.

Since a scavenging phenomenon that has occurred in the fourth control region disappears or is reduced as the exhaust pressure is increased, the valve overlap needs not to be generated. Accordingly, the controller 300 controls the EVC timing to be close to TDC.

Since the EVD is fixed in one form of the present disclosure, the controller 300 may control the EVO timing to an angle of approximately 40 to 50 degrees before BDC that is advantageous to exhaust pumping.

As described above, according to one form of the present disclosure, duration and timing of the continuous variable valve are simultaneously controlled, so the engine may be controlled under desired conditions.

That is, since opening timing and closing timing of the intake valve and the exhaust valve are appropriately controlled, the fuel efficiency under a partial load condition and power performance under a high load condition are improved. In addition, a fuel amount for starting may be reduced by increasing a valid compression ratio, and exhaust gas may be reduced by shortening time for heating a catalyst.

Since a fixed cam is used instead of a continuous variable valve duration device at the exhaust, production cost may be reduced with maintaining power performance.

While this disclosure has been described in connection with what is presently considered to be practical forms, it is to be understood that the disclosure is not limited to the disclosed forms, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the present disclosure.

The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure. 

What is claimed is:
 1. A method for controlling intake and exhaust valves of an engine, the method comprising: controlling, by an intake continuous variable valve timing (CVVT) device, opening and closing timings of the intake valve; controlling, by an exhaust CVVT device, opening and closing timing of the exhaust valve; determining, by a controller, a target opening duration of the intake valve and at least one of a target opening timing or a target closing timing of the intake valve and the exhaust valve, based on an engine load and an engine speed; modifying, by an intake continuous variable valve duration (CVVD) device, current opening and closing timings of the intake valve based on the target opening duration of the intake valve; and advancing, by the intake CVVD device, the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake valve by a predetermined value, or retarding the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve by a predetermined value, based on the target opening duration of the intake valve.
 2. The method of claim
 1. wherein the intake CVVD device advances the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake valve when the target opening duration of the intake valve is longer than a duration between the current opening timing and current closing timing of the intake valve.
 3. The method of claim
 1. wherein the intake CVVD device retards the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve when the target opening duration of the intake valve is shorter than a duration between the current opening timing and current closing timing of the intake valve.
 4. The method of claim 1, further comprising the step of adjusting, by the intake CVVT device, the current opening and closing timings of the intake valve to the target opening and closing timings of the intake valve, respectively.
 5. The method of claim 1, wherein, during the step of determining the target opening duration of the intake valve, the controller sets the target opening duration of the intake valve to a first intake opening duration in a first control region where the engine load is between first and second predetermined loads, and the controller controls the intake CVVD device to adjust a current opening duration to the first intake opening duration and controls a valve overlap between the intake valve and the exhaust valve in the first control region.
 6. The method of claim 5, wherein the current opening and closing timings of the intake valve are fixed and the closing timing of the exhaust valve is set as a maximum value capable of maintaining combustion stability in the first control region.
 7. The method of claim 1, wherein, during the step of determining the target opening duration of the intake valve, the controller sets the target opening duration of the intake valve to a second intake opening duration in a second control region where the engine load is greater than the second predetermined load and equal to or less than a third predetermined load, and the controller reduces a valve overlap by advancing the current closing timing of the exhaust valve via the exhaust CVVT device in the second control region.
 8. The method of claim 7, wherein a retardation amount of the current closing timing of the exhaust valve is reduced based on an increase of the engine load in the second control region.
 9. The method of claim 1, further comprising the step of advancing the current closing timing of the intake valve via the intake CVVT device according to an increase of the engine load in a third control region where the engine load is greater than a third predetermined load and equal to or less than a fourth predetermined load.
 10. The method of claim 1, further comprising the step of controlling, by the controller, a throttle valve to be fully opened; and controlling the current closing timing of the exhaust valve to be an angle after a top dead center (TDC) in a fourth control region where the engine load is greater than a fourth predetermined load and equal to or less than a fifth predetermined load and the engine speed is between first and second predetermined speeds.
 11. The method of claim 1, further comprising the step of determining a fifth control region when the engine load is greater than a fourth predetermined load and equal to or less than a fifth predetermined load and the engine speed is greater than a second predetermined speed and equal to or less than a third predetermined speed; and controlling, by the controller, a throttle valve to be fully opened and the current closing timing of the intake valve according to the engine speed in the fifth control region.
 12. The method of claim 11, wherein the target opening duration of the intake valve is increased according to an increase of the engine speed by retarding the current opening and closing timings of the intake valve in the fifth control region.
 13. The method of claim 11, wherein the exhaust CVVT device controls the current closing timing of the exhaust valve to be approximately at a top dead center so as to inhibit a valve overlap in the fifth control region. 